1. Field of the Invention
The present invention relates to a method and system for recovering data from a network element at a network management system (NMS), such as at NMS restart, or at re-establishment of communication after loss of communication with the NMS.
2. Description of the Related Art
Synchronous Optical Network (SONET) is a standard for synchronous data transmission over fiber optic networks. A common configuration of a SONET network includes optical fibers arranged in a ring topology, usually including two physical fibers, a working fiber and a protecting fiber. In order to communicate data over the fiber Ring, electro-optical devices are used to receive and transmit optical signal, receive and transmit electrical signals, and to convert data between optical and electrical signals. Typically, data is communicated electrically to such devices using a network protocol such as Ethernet, which is different than the SONET protocol. Thus, the device must perform data and protocol conversions as well as optical/electrical conversions.
One function block that is included in such a device is known as a MAC bridge. A media access control address (MAC address) is a unique identifier attached to most forms of networking equipment and which is typically used at the data link layer (Layer 2 of the OSI model). A network bridge is a device that connects multiple network segments along the data link layer. Thus, a MAC bridge may be used to connect an electrical network protocol, typically a local area network (LAN) protocol, such as Ethernet, to an optical network protocol used on the fiber Ring, such as SONET, at the data link layer.
Among the functions included in a MAC bridge is a filtering function known as a MAC bridge filter (MBF). Such a MAC bridge filter allows or prevents packets from passing through the MAC bridge based on the MAC address of the packet. This functional block is implemented to avoid unnecessary packet flooding on the Ring (optical) side as well as on LAN (electrical) side. It is designed to filter out the transit packets coming in from the Ring side but destined to other MAC stations on the ringlets. It can also prevent packets between LAN side local stations from entering the Ring.
A MAC address is 48 bits in length, thus, there are in total 2**48 MAC addresses. In reality, a MAC bridge database can store only a limited number of MAC addresses due to hardware resource limitations. For example, in a conventional MAC bridge filter hardware design, the bridge filter may be divided into 32K buckets with each bucket holding 4 MAC addresses with their associated Service Provider VLAN ID (SVID) and customer VLAN ID (CVID). The 12-bit SVID concatenated with the 12-bit CVID and 48-bit MAC address forms the unique entry for the filter, which is essentially a hash table addressed by this 72-bit string. A bucket overflow happens when there are already 4 entries in the bucket and another different 72-bit string is hashed into this bucket. Since the total number of entries contained in the hash table (128K in the above example) is much smaller than the total possible entries (272), MAC bridge bucket overflow is unavoidable. However, excessive bucket overflow results in poor bridge performance. Moreover, a hash function for a MAC bridge filter design should use as few hardware resources as possible. Therefore, a need arises for a hash function for a MAC bridge filter that improves bridge performance by reducing overflow of the MAC bridge database and which reduces cost of the device by using relatively few hardware resources.